Corrosion that occurs in an oil field environment is extremely complex and tends to attack all manner of metal equipment above and below ground. The principle corrosive agents found in the well fluids include hydrogen sulfide, carbon dioxide, oxygen, organic acids and solubilized salts. These agents may be present individually or in combination with each other. Valves, fittings, tubing, pumps, precipitators, pipe lines, sucker rods and other producing equipment are particularly susceptible. Deposits of rust, scale, corrosion by-products, paraffin and other substances create ideal environments for concentration cells. Carbon dioxide and hydrogen sulfide induced pitting is encouraged by such deposits. Acidic condensate that collects on metal tubing will also cause pitting. Extreme temperatures and pressures in downhole environments further accelerate corrosion.
Of all of the types of corrosion that occur in the oil field, pitting corrosion from hydrogen sulfide presents the most serious unsolved problem. Pitting is a form of corrosion that develops in highly localized areas on a metallic surface. It results in the development of cavities or pits that may range from shallow depressions to deep holes which may seriously affect the structural integrity of the metal equipment. Very often as oil fields mature and enhanced recovery methods such as water flooding are instituted, the concentration of hydrogen sulfide in the well fluids increases dramatically. This increase in concentration and its related effect on the extent of pitting corrosion may make older oil fields economically unattractive due to excessive corrosion costs.
Organic corrosion inhibitors are normally employed to control corrosion. But they are not very helpful in reducing pitting corrosion due to hydrogen sulfide.
Various surfactants have been employed for many years to improve the performance of organic corrosion inhibitor systems. Surfactants are generally added to inhibitor systems to perform the different functions of (1) solubilizing the corrosion inhibitor or other active ingredients, (2) cleaning the surface of the metal to be protected or treated, and (3) improving the penetration of the active ingredients into the microscopic pores of the metal. Ethoxylated alcohols and ethoxylated amines are the most common surfactants employed in corrosion inhibition systems. Two examples of such surfactant compounds are provied by U.S. Pat. Nos. 3,110,683 and 3,623,979. U.S. Pat. No. 3,110,683 discloses a series of alkylated, halogenated, sulfonated diphenyl oxides and U.S. Pat. No. 3,623,979 discloses a series of imidazolinyl polymeric acid amides. These representative examples of the prior art are effective in reducing the general effects of corrosion, but like the rest of the prior art, are unable to substantially reduce or eliminate hydrogen sulfide induced pitting.